In an electric vehicle using a motor as a driving source, motor cooling oil is often circulated by an electric oil pump to cool a stator or a rotor. However, if the electric oil pump is operated in to situation where the temperature of the motor does not rise at a low outside air temperature, mileage per charge is reduced. Therefore, a method that keeps the electric oil pump out of operation in this case has been suggested (e.g., see JP 2005-245085 A1).
According to another suggestion, when the outside air temperature is low, it is assumed that the viscosity of the cooling oil is high, and activation of the electric oil pump for circulating the motor cooling oil is attempted. Even when the electric oil pump cannot be activated by more than one attempt, the electric oil pump is not judged to be abnormal, so that erroneous detection of the electric oil pump abnormality is suppressed (e.g., see JP 2006-254616 A1).
In a system which supplies the oil pressure of control oil for a gearless drive mechanism, the oil temperature of the control oil may be lower than the oil temperature in an oil pan disposed in an oil temperature sensor. In this case, even when an oil temperature detected by the oil temperature sensor is an oil temperature that enables activation, the oil temperature of the control oil inside the oil pump which supplies the control oil pressure is not the oil temperature that enables activation, and a brushless motor for oil pump driving may step out. A method is thus suggested to activate the electric oil pump a predetermined time after the temperature of the control oil in the oil pan has reached the temperature that enables activation (e.g., see JP 2012-057645 A1).
Another method has been suggested. The oil temperature sensor has measurement error. Therefore, when it is not possible to judge whether the actual oil temperature is within a temperature range that enables activation of the electric oil pump in view of the measurement error, the fault judgment is invalidated, and trial running of the electric oil pump is carried out with a drive electric current and a desired rotation speed that are restricted compared with those in normal running. When a rotation speed equal to or greater than a predetermined rotation speed cannot be reached, the pump is deactivated. When the rotation speed equal to or greater than the predetermined rotation speed has been reached, the fault judgment is permitted, and the pump is driven under instruction. In this way, the accuracy of pump fault diagnosis is enhanced (e.g., see JP 2013-058267 A1).